The Osiris PHILter is a one channel active State Variable Biquad Filter, an outboard unit built by Osiris around the filter electronics originally installed in the Osiris bass, the instrument Phil Lesh played with the Grateful Dead. Pedal of the Day describes it as reverse engineered from those original filters, which the team thought lost for years before recovering them1. It sits among filter pedals, covering everything from deep low end tones to crispy high end tones depending on the filter type and Frequency setting1.
Where the circuit came from
The PHILter's story is tied closely to the Grateful Dead community. Pedal of the Day's reviewer, introducing the unit, wrote that "today's effect unit is up there at the top of the all-time list for me, as a basically life-long Deadhead"1. What the maker says about the circuit itself is that the Philter Volume mixed with the Direct Volume "allows for the deep low end tones or crispy high end tones, or anything between," depending on the filter type and the Frequency setting1. Beyond that, the filter section is produced as the outboard unit called the Osiris PHILter1.
Controls
| Control | What it does |
|---|---|
| Type Switch | Four way rotary switch selecting Low Pass, Band Pass, High Pass or Notch filter1 |
| Frequency Control | Sets the center frequency (FC) of the filter type used1 |
| Q Control | Sets the bandwidth of the center frequency selected1 |
| PHILter Volume | Sets the overall volume of the filter, independent of the Direct Volume1 |
| Direct Volume | Controls the dry signal's volume, independent of the PHILter Volume1 |
The two volume controls are the heart of how players use the pedal. The PHILter Volume and the Direct Volume can be used at the same time, alone, or as a mix that stays in phase with each other1. Pedal of the Day notes that this blending "allows for the deep low end tones or crispy high end tones, or anything between" depending on the filter type and Frequency setting1.
What reviewers said
Pedal of the Day's reviewer, writing in March 2025, placed the pedal in rare company: "today's effect unit is up there at the top of the all-time list for me, as a basically life-long Deadhead"1.
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Questions
What is the Osiris PHILter based on?
The PHILter is reverse engineered from the original filters and electronics installed in the Osiris bass, also known as Mission Control, the instrument Phil Lesh played with the Grateful Dead. The Osiris team acquired the bass in December 2019 and the original filters and electronics in March 2024, then extracted the filter section into an outboard unit.
What filter types does the Osiris PHILter have?
A four way rotary Type Switch selects between Low Pass, Band Pass, High Pass and Notch filter positions. The Frequency Control then sets the center frequency of whichever filter type is selected, and the Q Control sets the bandwidth of that center frequency.
Can I blend the dry signal with the filtered signal on the PHILter?
Yes. The PHILter Volume and the Direct Volume can be used at the same time, alone, or as a mix that stays in phase with each other. The Direct Volume controls the dry signal's volume independently of the PHILter Volume, which sets the overall volume of the filter.
What does the Q control do on the PHILter?
The Q Control sets the bandwidth of the center frequency selected by the Frequency Control. In practice it shapes how narrow or broad a band of frequencies the filter emphasizes or cuts around the chosen center point.
Is the Osiris PHILter a stereo pedal?
No. The Osiris PHILter is described as a one channel active State Variable Biquad Filter, so it processes a single channel rather than offering stereo operation.
Sources (1)
- Osiris PHILter State Variable Biquad Filter, Pedal of the Day, 2025-03-28